Method of producing metal powders



Patenterl' Apr.- 14, 1936 UNITED STATES METHOD OF PRODUCING METALPOWDERS Walter Zeiss, Berlin-Charlottenburg, Germany No Drawing.Application November 1, 1934,

Serial No. 751,035 1933 1': Claims. (01. -22) This invention relates tothe production of metal powders, more particularly to .a new and moreeconomical method of producing such powders.

Metal powders have been prodiced in such a manner that the correspondingmetals are vaporized and that the metal powder was precipitated from thevapor by rapid cooling. This process, however, showed a great number ofdisadvantages among which especially the necessary high temperaturecaused difficulties in technical operation.

According to the present invention these disadvantages are avoidedwhereby metal powders of excellent qualities are obtained in a simplemanner. The process consists inintimately mixing the molten metal with afine-grained, solid and hard material, for instance, sand, at the sametime taking care by introducing inert gases, such as nitrogen and thelike that no oxidation of the metal takes place.

The dispersion. thus produced from the molten metal and the grainy hardmaterial, thereupon, is cooled while intimately and continuously mixingand the mixture obtained thereby is used either as such or the metalpowder is separated from the dispersing agent. This separation may becarried out, for instance, by physical methods, as by sifting, sieving,elutriating, and the like.

The pure metal is especially suitable as starting material, but alsometal alloys and, when working, for instance, in the presence of areducing gas, also fusible metal compounds capable of reduction can beused. As dispersing agent there may be employed those materials which donot exhibit any change of form (deformation) at the temperature of thefused metal, such as, for instance, fine-grained sand or other minerals,various other kinds of rocks or even artificially produced solidmaterials, such as glass, porcelain, carbides and the like. Even metalsor metal compounds, insofar as they do not react with the metal to bepulverized, can be used for this purpose. In case metal compounds whichare dispersed in a reducing atmosphere are used as starting material, asdispersing agent there may be employed a catalytically acting agentwhich accelerates the reduction, for instance, hard but still porouspieces of porcelain which are impregnated with a catalyst capable ofaccelerating the reaction.

It is advisable to select as a dispersing agent a material the size ofthe separate grains of which varies between 2 and 3 mm. in diameter; fortherewith the best results are achieved. But the In Germany November 1,

use of a dispersing agent of coarser grain has the advantage that theseparation of the metal powder from the dispersing agent in an airseparator and even in a sieving device can be carried out with a bettereffect and more readily than with a dispersing agent of finer grain.

Furthermore it has been found that the size of the grains of the metalpowder can be varied depending upon the use of larger or smaller amountsof the dispersing agent with respect to the metal. Extremelyfine-grained powders are obtained on employing larger quantities of thedispersing agent. Such metal powders possess a high setting and pouringvolume. On decreasing the amount of the dispersing agent in the mixture,more coarse-grained products are obtained which possess a low settingand pouring volume.

When starting with metal compounds and converting the same into metalsby reduction, it is frequently of advantage first to produce the oxidesfrom said compounds by treating the same with oxidizing gases, and thento convert the oxides into the metals by further treatment with reducinggases. It has been found that in some cases it is of advantage toincompletely reduce the metal oxide. Thereby the very bothersomesticking of the metal to the dispersing agent is avoided. In order toproduce therefrom the oxide-free metal, the small quantities of oxidepresent in the powderafter such a treatment and the separation from thedispersing agent can be readily removed by treatment with hydrogen.

' The observation that the presence of small quantities of the oxideprevents the sticking to the dispersing agent can also be made use of bymixing small amounts of oxygen orgases containing oxygen to the inertgases on dispersing the molten metal. It has been found that the metalpowders obtained thereby which contain metal oxide, are especiallysuitable for the purposes of the accumulator or storage batteryindustry. The same result is achieved by exposing the molten metal incontact with the dispersing agent for a brief period of time to a streamof air in such a manner that complete oxidation of the metal cannot takeplace.

The temperature on dispersing the liquid metal is preferably about 50 toabove, the melting.

point of the starting material to be transformed into a powder. Whenproducing themetal pow-j der by reducing the metal compoundsit rnaysometimes be. of advantage to operate under pressure. The solidificationof the dispersion .canbe effected by simplecooling or by the,acjztidn}ota cold gas or air current. The separation of the dispersingagent from the metal powder can be carried out by any chemical orphysical method. The air separation process has proved to be especiallyadvantageous, but also other methods, such as sieving, centrifuging,elutriating or even dissolving the dispersing agent may be employed.

Example 1 200 kg. of sand and 200 kg. of metallic lead are heated abovethe melting point of the lead in a container provided with a stirringdevice. When the lead is molten, the stirring device is caused tooperate. Thereupon an air current is passed for A to hour through theapparatus at a temperature of about 440 C. The mixture is allowed tocool while stirring and the slightly oxidizedJead powder is separatedfrom the sand by air separation. The lead powder obtained therebyrepresents an excellent material for the purposes of the storage batteryindustry. On suitable selection of the reaction conditions andcorresponding proportioning of the oxygen supply a lead powdercontaining varying amounts of lead oxide, as required, can be obtained.

In order to produce lead powder itself, the process is preferablycarried out in the atmosphere of an inert gas, such as nitrogen to whichsmall amounts of oxygen or air are admixed in order to prevent thesticking of the lead to the sand. In order to obtain a pure metal powderthe reaction product is subjected to a treatment with hydrogen at atemperature below the melting point of the lead before or afterseparation of the sand.

Of course, one may also proceed in such a manner that the sand isstirred into the molten lead or that the molten lead is allowed totrickle into the sand heated to about 400-600 C., while stirring thesand.

When using about 300 kg. of sand for 200 kg. of metallic lead in thisexample, a finer grained product than described is obtained, while byusing only 100 kg. of sand for 200 kg. of lead a coarser grained powderresults.

Example 2 Antimony sulfide is mixed with the same amount by weight ofunglazed porous stoneware grit and is stirred in the presence of air atabout 700 C. Antimony oxide of the melting point 656 C. is formedwhereby sulfur dioxide is evolved. Thereupon, while maintaining the sametemperature, hydrogen is passed over the mixture of antimony oxide andstoneware grit until the reduction to antimony is completed. Theantimony is separated from the grit by sieving off the former. Therebyan antimony powder of dark color is obtained. The air or the oxygen inthe first reaction step and the hydrogen in the second reaction step canbe introduced also under pressure. The stoneware grit can furthermore beimpregnated with materials which are capable of catalyticallyaccelerating the oxidation as well as the reduction.

Example 3 Molten zinc is intimately dispersed with granulated iron inthe presence of an inert gas, such as nitrogen, until it is transformedinto a finely divided, extremely reactive zinc powder which can be usedeither in mixture with the iron or after separation from the latter.

Other metals than those mentioned in the examples, such as tin, bismuth,cadmium andthe like, can also be converted very readily, and in a simpleand convenient manner into powder.

While. I have described my invention setting forth several embodimentsthereof, it is not limited thereto as variations in the procedure may beused within the spirit of the invention. Other metals than those namedare amenable to the treatment. The time and temperature of treating maybe varied at will, the character of the dispersing agent may be changed,the means for stirring the metal and dispersing agent may be of anysuitable type and the separating means may be other than thosespecifically described above. These and other variations, which will beapparent to those skilled in the art, may be made in my invention, thescope of which is defined in the claims appended hereto.

What I claim is- 1. A method of producing metal powders which comprisesproviding a mixture of a molten metal and a solid dispersing agent whichis not deformed at the temperature of operation, stirring said mixture,and cooling the same to solidify the metal into powder form during saidstirring.

2. A method of producing metal powders which comprises providing amixture of a molten metal and a solid dispersing agent which is notdeformed at the temperature of operation, stirring said mixture, andcooling the same to solidify the metal into powder form during saidstirring and separating said powder from said dispersing agent.

3. A method of producing metal powders which comprises providing amixture of a molten metal and a solid dispersing agent which is notdeformed at the temperature of operation, stirring said mixture in thepresence of an indifferent gas, and cooling the same to solidify themetal into powder form during said stirring.

4. A method of producing metal powders which comprises providing amixture of a molten metal and a solid dispersing agent which is notdeformed at the temperature of operation, stirring said mixture in thepresence of an amount of oxygen capable of partially oxidizing saidmetal, and cooling the same to solidify the metal into powder formduring said stirring.

5. A method of producing metal powders which comprises providing amixture of a molten metal and a solid dispersing agent which is notdeformed at the temperature of operation, stirring said mixture in thepresence of an indifferent gas containing oxygen.

6. A method of producing metal powders which comprises providing amixture of a molten metal and a solid dispersing agent which is notdeformed at the temperature of operation, stirring said mixture in thepresence of an amount of oxygen capable of partially oxidizing saidmetal, and cooling the same to solidify the metal into powder formduring said stirring, separating said powder from said dispersing agentand subjecting said powder to reduction.

7. A method of producing metal powders which comprises providing amixture of a molten metal containing metal oxide and a solid dispersingagent which is not deformed at the temperature of operation, stirringsaid mixture, and cooling the same to solidify the metal into powderform during said stirring.

8. A method of producing metal powders which comprises providing amixture of a molten metal and a solid dispersing agent which is notdeformed at the temperature of operation and having a diameter of about2-3 mm., stirring said mixture, and cooling the same to solidify themetal into powder form during said stirring.

9. A method of producing metal powders which comprises providing amixture of a molten metal at a temperature about 50-100 C. above itsmelting point and a solid dispersing agent which is not deformed at thetemperature of operation, stirring said mixture, cooling the same tosolidify the metal into powder form during said stirring.

10. A method of producing metal powders which comprises providing amixture ofa molten metal and a solid dispersing agent which is notdeformed at the temperature of operation, stirring said mixture, andcooling the same to solidify the metal into powder form during saidstirring, and varying the amount of said agent, whereby the diameter ofthe resulting powder is inversely varied.

11. A method of producing metal powders which comprises providing amixture of a metal oxide and a solid dispersing agent which is notdeformed at the temperature of operation, heating the same to atemperature above the melting point of the metal in the presence of areducing agent, stirring said mixture, and cooling the same to solidifythe metal into powder during said stirring.

12. A method of producing metal powders which comprises providing amixture of a metal oxide and a solid dispersing agent which is notdeformed at the temperature of operation, heating the same to atemperature above the melting point of the metal in the presence of areducing agent under pressure, stirring said mixture, and cooling thesame to solidify the metal into powder during said stirring.

13. A method of producing metal powders which comprises providing amixture of a metal compound and a solid dispersing agent which is notdeformed at the temperature of operation, heating the same underoxidizing conditions to form the metal oxide, heating under reducingconditions to form the metal, the temperature being above the meltingpoint thereof, stirring said mixture, and cooling the same to solidifythe metal into powder during said stirring.

14. A method of producing metal powders which comprises providing amixture 01' a metal compound and a solid dispersing agent which is notdeformed at the temperature of operation, heating the same underoxidizing conditions'to form the metal oxide, heating under reducingconditions to incompletely reduce the oxide into the metal, thetemperature being above the melting point thereof, stirring saidmixture, and cooling the same to solidify the metal into powder duringsaid stirring.

15. A method of producing metal powders which comprises providing amixture of a metal compound and a solid dispersing agent which is notdeformed at the temperature of operation, heating the same underoxidizing conditions to form the metal oxide, heating under reducingconditions to incompletely reduce the oxide into the metal, thetemperature being above the melting point thereof, stirring said mixtureand cooling the same to solidify the metal into powder during saidstirring, separating the powder and completing the reduction of oxide tometal.

16. A method of producing metal powders which comprises providing amixture of a molten metal and a. solid dispersing agent which is notdeformed at a temperature of operation, the amount of said agent beingsumcient to render the resulting mass non-liquid, stirringsaid mixtureto coat said agent with a film of, said metal and cooling said mixtureto solidify said metal.

17. A method of producing metal powders which comprises providing amixture of a molten metal and a solid dispersing agent which is notdeformed at the temperature of operation, the amount of said agentbeingsuflicient to render the resulting mass non-liquid, stirring saidmixture to coat said agent with a film of said metal and cooling saidmixture to solidify said metal, the shrinkage of said metal during saidsolidification causing the film to crack ofi of said agent and to form apowder.

WALTER ZEISS.

